Exercise as a Teen May Offer Lifelong Benefits

Get thee to a gym?

Action Points

Note that this Chinese population study found associations between higher amounts of adolescent and adult exercise and better overall survival, CVD mortality, and cancer mortality.

Be aware that the study was limited by recall bias.

Girls who exercise may be banking a lifetime benefit: lower risks of cardiovascular disease (CVD), cancer, and premature death as adults.

In a prospective cohort study of 74,941 Chinese women age 40 to 70, women who said they exercised only as adolescents appeared to have a lower risk of all-cause mortality (HR 0.82, 95% CI 0.73-0.91) than women who didn't start exercising until adulthood (HR 0.87, 95% CI 0.81-0.94). Women who exercised throughout adolescence and adulthood had the smallest incidence of all-cause mortality (HR 0.80, 95% CI 0.72-0.89).

But the differences were small, which may indicate a simpler explanation: exercise is good at all ages, but starting in youth may provide an additive benefit.

Lead author Sarah Nechuta, MPH, PhD said SWHS "collected information on lifestyle factors both in adolescence and during adulthood," which isn't common, "so they provide a very unique opportunity to be able to investigate adolescent exercise in relation to adult mortality."

Participants completed surveys to provide detailed information about past and present lifestyle habits, including diet and exercise at age 13 to 19. Researchers followed up with participants every 2 to 3 years for an average of 12.9 years, after which 5,282 died: 2,375 of cancer and 1,620 of CVD.

Their first statistical analysis adjusted for birth year, age at menarche, adolescent diet, and BMI. Two additional models adjusted for socioeconomic factors, leisure activities, diet, and BMI in adulthood, and baseline chronic disease history. Though the numbers varied slightly with these adjustments, the overall trends remained the same.

"It's good to have the evidence and it's good to have these numbers, but I'm not surprised that physical activity turned out to be a good thing," said Andrew Rundle, PhD, an associate professor of Epidemiology at Columbia University.

"Cardiovascular health and cholesterol and hypertension are also influenced by childhood and adolescent physical activity," Rundle said.

"It's important to consider the accumulated risk of cancer and protective factors over the life course since we know that many health behaviors "track" from early childhood to adolescence to adulthood," said Bernard Fuemmeler, MPH, PhD, an associate professor of community and family medicine at Duke University.

He said the current study "is important because they were able to show data to support what many have suspected – that adolescent health behaviors, especially physical activity, is related later adult health," Fuemmeler added.

Nechuta et al. did acknowledge that the main limitation for this study was the self-reported information about lifestyle habits, because they asked older women to recall from memory details about their adolescence. They also didn't have details about the type of exercise performed -- only the hours per week they spent exercising.

However, she also said that these results "most likely underestimate the impact of adolescent exercise," because their analysis didn't include data on daily occupational activities, like walking or biking to school or work.

Though recalled information could have biased results, Fuemmeler said that "a large prospective study where data on physical activity was collected during adolescence and mortality was assessed in later decades of life is not really feasible. The study, with some of its limitations, further advances what many have suspected – that child and adolescent lifestyles are important for health over the life course."

The mechanisms behind this lifelong effect are unknown. According to the CDC, "Regular physical activity in childhood and adolescence improves strength and endurance, helps build healthy bones and muscles, helps control weight, reduces anxiety and stress, increases self-esteem, and may improve blood pressure and cholesterol levels." Yet only one-quarter of high school students meet the CDC's recommended 60 minutes of exercise daily.

Fuemmeler wrote that adolescent exercise likely plays a role in reducing the risk for obesity, "thereby reducing the risk for obesity-related cancers." But it "may also play a more direct role in regulating inflammatory markers and hormones that help protect against the development of cancer risk over the life course."

Nechuta said that the next step with the current available SWHS data is to look at the incidence of chronic diseases before mortality.

Replicating the findings is important to increase confidence in the results, Fuemmeler added. "We also must do more work to improve the health of children and adolescence, since studies like this and others suggest that intervening early in the life course has immediate benefits on child and adolescent health, but intervening early may also have long term benefits on our risk for chronic disease and cancer as we mature through adulthood."

Rundle said that this research is important for public health because "if we can generate data showing that physical activity in adolescence is health beneficial independent of what you do later, that provides the kind of data and evidence that people require to put policies in place."

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